Compact keratoscope with interchangeable cones

ABSTRACT

A keratoscope image processing system having a compact keratoscope usable with a variety of light ring cones employs an improved cone and lightbox combination in which the light transmitting rings of the cone are more sharply defined by being positioned between incised opaque rings, and in which the lightbox has facets for mounting and heat-sinking a pair of laser diodes, a semi-toroidal cavity for mounting a ring-shaped fluorescent lamp for illuminating the cone and tunnels that direct the laser beams into the cone to intersect on the visual axis of the cone. The light box provides a surface for fixedly mounting a pair of mirrors that redirect the laser beams. The different cones are identified by patterns of light pervious spots illuminated from the lightbox and sensed by detectors mounted in the lightbox. Signals from the detectors modify the image processing in accordance with stored optical characteristics corresponding to the detected patterns.

This application is a continuation-in-part of an application entitled"ILLUMINATED RING DEVICE", Ser. No. 07/492,939, Filed Mar. 13, 1990, nowU.S. Pat. No. 5,018,850, and of an application entitled "INTERCHANGEABLEKERATOSCOPE DEVICE", Ser. No. 07/496,016, Filed Mar. 20, 1990, now U.S.Pat. No. 5,009,498, by the same inventors.

TECHNICAL FIELD

This invention relates to instruments for examining the topography ofcurved reflective surfaces, and more particularly, to such instrumentsknown as keratoscopes.

BACKGROUND ART

Keratoscope instruments of the Placido disc type have long been used byophthmologists for examining the surface curvature of the human eye. Amore modern form of such instrument is disclosed in U.S. Pat. No.3,797,921 issued Mar. 19, 1974 to L. G. Kilmer et al. The size of thePlacido disc instrument is determined by the number of concentric lightrings, or mires, to be projected onto the patient's eye and the morelight rings that are to be projected in the vicinity of the limbus, thegreater the diameter of the instrument must be. However the greater thisdimension the more it tends to block eye contact between the patient andthe ophthalmologist thereby causing certain patients some amount ofemotional discomfort.

An improved form of apparatus for mapping the contours of the cornea isshown in Gersten, et al, U.S. Pat. No. 4,863,260 issued Sep. 5, 1989.The apparatus described in the Gersten '260 patent employed acylindrical form of keratometer containing a plurality of illuminatedrings incised along the opaquely coated bore of a conical translucentplastic body. The incised rings of the bore were illuminated by an arrayof incandescent lamps contained in a lightbox disposed adjacent to thebase of the cone. Toward the apex of the cone converging beams from apair of helium-neon laser guns established an optical reference point onthe visual axis of the apparatus. For the precise location of the pointof laser beam intersection it was desired to have the beams intersect atan appreciable angle of at least 90 degrees. Achieving this angle ofintersection required that the laser guns either be positioned at thisangle to the visual axis or that a mirror arrangement be employed. Ineither case the transverse dimension of the apparatus was increased.

As mentioned above, the illuminated rings of the Gersten et al '260patent were formed by cutting through the opaque coating of the bore toexpose the translucent plastic. Variations in the thickness of theopaque coating and in the sharpness of the tools used to cut through theopaque coating affected the regularity of the edges defining theilluminated rings and consequently the distinctness of the rings' imageprojected on the target. In addition, the plastic cone exhibited asubstantial thermal coefficient of expansion. The array of incandescentlamps required to provide sufficient illumination to the base of theconical body to illuminate the incised rings could generate considerableheat. The expansion of the cone could shift the location of the ringpattern relative to the focal point of the instrument necessitating thatthe apparatus be recalibrated after warm-up. In addition, if it weredesired to substitute a cone having a different ring pattern ordifferent bore diameter a painstaking re-alignment of the laser beamguns and mirrors with respect to the visual axis of the apparatus wouldbe required. Such substitution also would require re-programming of thecomputer controlling the mapping of the eye contour.

SUMMARY OF THE INVENTION

A more compact and versatile computer-controlled keratoscope system forproducing sharper ring patterns and having the ability to employ aninterchangeable variety of cones is provided through the use astructurally rigid lightbox which serves not only as a mounting for thedifferent cones but which houses an improved light source and laser beamdevices in such a manner as to eliminate any need for re-programming orsubsequent adjustment by the user. The lightbox includes a polished,semi-toroidal concavity on its anterior face toward the base of thecone. A circular fluorescent lamp is positioned in the toroidalconcavity so as to direct the lamplight toward the base of the cone. Theopposite face of the lightbox provides facets for fixedly aligning apair of laser diodes at a desired degree of inclination to the visualaxis of the apparatus. Light beams from the laser diodes are conductedthrough a first pair of tunnels in the lightbox which lead to mirrorsfixedly attached to an exterior surface of the lightbox. The mirrorsredirect the laser beams into a second set of tunnels bored through thelightbox which are aligned with a third set of tunnels bored through thebody of the plastic cone. The third set of tunnels lead the beam tointersect at the desired predetermined point on the visual axis of theapparatus.

In this illustrative embodiment, the predetermined alignment of thediodes, tunnels, mirrors, and the conical body made possible by thestructurally rigid lightbox eliminates the need for alignment of theinstrument by the user. Moreover, different conical bodies can beemployed in the apparatus without require any adjustment in thealignment of the positions of the lasers, the point of intersection oftheir beams being unchanged.

Further in accordance with the principles of the present invention theinterchangeability of the cones is facilitated by having each coneinclude a distinctive pattern of illuminated machine-readable indicatorspots. The indicator spots are positioned so as to be illuminated fromthe lightbox and arranged in a code indicative of the calibrationcharacteristics of the cone. The lightbox includes an array ofphotodetectors that are energized by the illuminated spots to indicateto the computer system a binary coded combination that identifies theparticular type of cone that is in place.

In the illustrative embodiment, the light transmitting rings of the coneare not incised through the opaque coating. Instead, a series of ringsare incised into a bare bore which is then opaquely coated, filling theincised rings. The bore is then reamed or slightly enlarged by machiningto form uncoated, light-transmitting lands from which the coating hasbeen removed between the incised rings. The walls and floor of theincised rings retain the opaque coating rather than the lands betweenthe incised rings as in the prior art. Accordingly the thickness of theretained opaque coating is not as critical and the edges of the lighttransmitting rings are more sharply defined.

BRIEF DESCRIPTION OF DRAWINGS

A more complete understanding of the invention can be obtained from aconsideration of the following detailed description and the appendedclaims in conjunction with the attached drawings in which:

FIG. 1 shows a keratoscope system including a top, cross-sectional viewof an improved cone and lightbox;

FIG. 2 is an enlarged detail showing the rings of the cone of FIG. 1;

FIG. 3 is an enlarged cross-sectional view of the coded aperture disk ofFIG. 1;

FIG. 4A is a front view of the anterior surface of the lightbox of FIG.1;

FIG. 4B is a detail of the mechanism for retaining the interchangeablelight cones;

FIG. 5 is a process flow diagram for responding to the cone typeindicator signals; and

FIG. 6 is a diagram of image data scanning parameters used in FIG. 5.

DETAILED DESCRIPTION

FIG. 1 shows a computer-controlled keratoscope system having an improvedcone 13 and lightbox 23. Target 11 is located at the apical end of cone13 and is schematically indicated by a circle to represent thereflective surface of a calibration ball or the cornea of a patient'seye whose surface contour is to be mapped. A camera 27 acquires thetwo-dimensional image reflected from target 11. Computer-controlledsubsystem 47 comprises a microcomputer 46, video monitor 49, frame store48 and computer monitor 50 which displays a menu for guiding theoperator through the processing steps.

The top cross-sectional view of cone 13 and lightbox 23 is taken along ahorizontal plane through the visual axis 12. Cone 13 is fabricated oftranslucent plastic material and contains a central longitudinalcylindrical passageway 21 which is lined with a set of succesiveilluminated rings 20 and opaque rings 24. The illuminated rings cause acorresponding set of illuminated mires to reflected from the reflectivesurface of target 11.

The exterior of cone 13 is provided with an inner, light reflectivecoating 17 and an outer opaque coating 18 to reflect as much of thelight entering the base of the cone to the central passageway 21 so asto provide maximum illumination of rings 20.

The light-transmitting rings 20 of cone 13 are advantageously fabricatedby first incising the series of annular rings 24 in central passageway21, then coating the passageway with an opaque material, preferablyblack in color. The diameter of the passageway is then bored out to adepth less than that of the incised rings 24. This removes the opaquecoating from the minor diameter of the passageway leaving a series ofuncoated lands between the incised rings. The sidewalls and floors ofthe incised rings, however, retain the opaque coating.

In addition to the illuminated rings 20 provided along the bore 21, cone13 may also advantageously be provided with an opaquely coatedtranslucent disc 22 near its base end upon which one or more clear rings22R (see FIG.3) may be provided. In addition, the base end of cone 13may advantageoulsy contain a chamfered, uncoated extension portion 29adjacent to the last of the translucent rings 20 which will lightdirectly from lamp 16.

At the base of the cone 13 an aluminum lightbox 23 contains asemi-toroidal concavity 31 having a highly polished, reflective,interior surface. A circular fluorescent tube 16 is mounted in theconcavity 31 and the reflective surface directs the light toward thebase of cone 13.

An additional refinement is present in FIG. 1 in that fluorescent tube16 and camera 27 may advantageously be chosen so that the phosphoremployed in tube 16 is properly coordinated with the spectral responseof the chip employed in camera 27. Matching the spectral responsesprovides better sensitivity of camera focus. However, it is important ina corneal measuring device that focus be achieved within the visiblelight spectrum. For example, where camera 27 employs a CCD chip, itsspectral response may be found to be peaked toward the infra-red end ofthe light spectrum. Since it is undesirable to base corneal imagemeasurements on infra-red response, the use of a fluorescent phosphor intube 16 which produces no infra-red output is highly desirable. Inaddition, the color of the phosphor may advantageously be specified asgreen because the reflectivity of the human iris is lower for green sothat the corneal image will have a "blacker" background between theilluminated rings due to the reduced amount of reflection than wouldoccur with a white phosphor.

The image of the mires appearing on target 11 is reflected, back alongthe passage 21 through the central aperture of translucent disk 22 andthe central aperture 32 of lightbox 23. The image is detected by camerasubsystem including an extension tube 26, a camera 27, and a lens 28,all also coaxial with the visual axis 12. Camera 27 is advantageouslyfocused at the focal point of the reflective surface of target 11,rather than the end 41 of cone 13 in order accurately to capture all ofthe rings reflected from the cornea.

To accommodate targets of different diameter and to project differentkinds of ring patterns, different kinds of cones are required. Thenumber of rings to be projected on the target is determined by thelength and diameter of cone 13. In order to distinguish automaticallyamong the different types of cones that may be mounted to lightbox 23,each cone is provided with a an opaquely coated aperatured plastic disk22 having a distinctive plurality of binary-coded markings 22DC on itsright-hand side. Such markings are provided by selectively removing aportion of the opaque coating 22C of disk 22 except at selected ones ofthose coded locations necessary to indicate which of plural conical bodytypes is in place. When fluorescent tube 16 is energized, the interiorof aperatured disk 22 is illuminated and photosensors 30 mounted in thelightbox 23 respond to the pattern of illumination provided by thebinary coded markings 22DC on disk 22.

A pair of laser diodes 33 are mounted on respective facets or bosses 52on the posterior face of lightbox 23 opposite concavity 31. Laser diodes33 have their longitudinal axes in a common plane with the visual axis12 and are located as close as possible to axis 12 so that thekeratoscope can have small lateral dimensions. Facets 52 are oriented sothat the beams from the lasers 33 are angled away from the axis 12.Light beams from lasers 33 are projected through a first set of tunnels37 bored in lightbox 23. The beams emerge at the periphery of lightbox23 where they are reflected by mirrors 38 into a second set of tunnels39 aimed at intersection point 41 on visual axis 12. Mirrors 38 areadhesively bonded to the exterior surface lightbox 23.

Tunnels 39 are collinear with a third pair of tunnels 40, respectively,in cone 13. Tunnels 40 are in the same common plane with axis 12.Tunnels 37 and 39 are angled so that mirrors 38 will steer the laserbeams from tunnels 37 through tunnels 39 and 40 to predeterminedintersection point on visual axis 12. Since beams from lasers 33 areenclosed within a series of tunnels whose alignment is fixed, they arenot subject to misalignment nor are they subject to externalinterference.

Laser diodes 33 generate some heat and their characteristics have someknown temperature sensitivities. The thermal mass of aluminum lightbox23 in conjunction with the use of thermally conductive mounting brackets36 provide an effective heat sink to stabilize the temperature of thediodes. Each of the lasers 33 is connected to the tap terminals of apotentiometer 42 at the output of a laser power supply 43 to determinethe operating power level of the lasers.

Suitable diode lasers are presently commercially available from severaldifferent manufacturers. One such diode laser operates at a wavelengthof 670 nanometers, well within the visible spectrum, and an output powerof about ten microwatts. Coherent beam waist diameter is about 270microns. The laser is in a gold plated metallic housing that is about2.5 centimeters long, including internal focusing optics.

It can be seen from the foregoing description that lightbox 23 providesa platform providing common support for a group of keratoscope partsincluding cone 13, circular fluorescent light tube 16, photosensors 30,lasers 33, and mirrors 38.

While FIG. 1 shows a top cross-sectional view of lightbox 23 in order tobest illustrate tunnels 37 and 39, FIG. 4A shows a frontal view oflightbox 23. At the "6-o'clock" position of lightbox 23, a singlelocating key 19 engages a slot in the base of cone 13 to radially orientcone 13 in lightbox 23. At the "12-o'clock" "4-o'clock" and "8-o'clock"positions of lightbox 23 a banking pin 35 and a spring loaded detentball (shown in FIG. 4B) removably secure cone 13 in lightbox 23. Therelationship of the lightbox's detent ball 25B, spring 25S, andretaining set screw 25SS with the base of cone 13 is shown in FIG. 4B.At the "9-o'clock and "3-o'clock" positions in the rim of lightbox 23are seen the ends 61 of tunnels 37 and 39 of FIG. 1 where these tunnelsmeet at mirror-mounting flats 34. At the "12-o'clock" position oflightbox 23 a pass-through hole 54 accommodates the ends (not shown) ofthe fluorescent tube 16 so that electrical connections (not shown) canbe made without throwing shadows onto the base of cone 13. Tube 16(FIG. 1) is advantageously fixed in place within the concavity 31 withseveral dabs of silicone glue. Central opening 32 provides for thepassage of light along the visual axis 12 as shown in FIG. 1. Throughinternal rim 58 four holes 25 are provided for retaining thephotosensors 30 (of FIG. 1).

FIG. 5 is a process flow diagram illustrating one way to incorporate theuse of coded indicator spots 22DC into one well-known radial scanningroutine for keratoscopic image data processing. Reference characters inparentheses correspond to similarly designated steps in FIG. 5. FIG. 6is a diagram to facilitate consideration of FIG. 5 and shows anarbitrary radius ri extending from a center point at the X-Y axisorigin, at an arbitrary angle φi with respect to the X-axis. That centerpoint represents a central point in an image. Image data points for alast-ring Ri are also shown.

At the start of the FIG. 5 process, outputs of photosensors 30 aresampled (56) and tested to ascertain correct cone type (57) by usinguser-provided initializing input data stored in the memory ofmicrocomputer 46. If it is not one for which data has been stored, anerror message is displayed (58); and the process is interrupted untilcorrective action is taken. If the proper ring device type is in place,the value represented by the binary coded, detector states informationis translated (59) to obtain a last-ring count value for the particularapplication involved and which count will be used to limit the extent ofscanning along different radii from a predetermined display center pointto locate intersections with reflected images of illuminated rings 20.

An initial radius scan is begun (60). At successive points along theradius ri, image picture element intensity values are compared to detect(61) intersections with reflections of bright illuminated rings 20. Ifno intersection is detected the test location is incremented out alongthe radius to make a new test. If an intersection is detected, a countof intersections found so far in the scan is compared (62) to thelast-ring count from step (59). If the last-ring Ri has not beenreached, the intersection data is processed (63); and the scan locationis incremented again. If the last ring has been reached, the radiusangle φi is incremented (64) and the new angle checked (65) to seewhether or not a full circular scan has been completed. If it has, theprocess ends; but if it has not, a scan from center at the new radiusangle is begun (60).

Although the invention has been described in connection with aparticular embodiment thereof, other applications, embodiments, andmodifications which will be apparent to those skilled in the art areincluded within the spirit and scope of the invention.

What is claimed is:
 1. A keratoscope image processing system forprocessing an image reflected upon a target, said system comprising alightbox and a conical body of translucent material, said conical bodyhaving an integral cylindrical bore including a base portion, saidcylindrical bore defining a series of successive opaque and lighttransmitting rings for reflection upon said target, said opaque ringsbeing incised in said cylindrical bore and filled with an opaquecoating, and said lightbox including a semi-toroidal concavity foraccommodating a toroidal light source and for maintaining said lightsource substantially at the focus of said concavity, thereby to causesubstantially all of the light from said light source to be transmittedtoward the base portion of said conical body.
 2. A keratoscope imageprocessing system according to claim 1 wherein said light source is afluorescent lamp.
 3. A keratoscope image processing system according toclaim 1 wherein said lightbox for accommodating said light source is analuminum housing and wherein said semi-toroidal concavity is providedwith a specular reflective surface.
 4. A keratoscope image processingsystem according to claim 3 wherein said lightbox includes a recess forreceiving the base portion of said conical body and a plurality ofspring-loaded detents for removably securing said conical body in saidrecess.
 5. A keratoscope image processing system according to claim 1wherein said lightbox for accommodating said light source is an aluminumhousing having an articulated facet for mounting and heat-sinking adiode laser.
 6. A keratoscope image processing system according to claim5 wherein said lightbox includes a first tunnel leading from saidarticulated facet for passage of a laser beam from said laser throughsaid conical body.
 7. A keratoscope image processing system according toclaim 6 wherein said lightbox includes a second tunnel adjoining saidfirst tunnel and a mirror positioned at the junction of said first andsecond tunnels.
 8. A keratoscope image processing system according toclaim 7 wherein said conical body includes a third tunnel, the axis ofsaid third tunnel being adapted to be aligned with the axis of saidsecond tunnel of said lightbox.
 9. A keratoscope image processing systemaccording to claim 8 wherein the axes of said second tunnel of saidlightbox and said third tunnel of said conical body aim at apredetermined point in said bore.
 10. A keratoscope image processingsystem according to claim 6 wherein the axis of said first tunnel isperpendicular to said articulated facet.
 11. A keratoscope imageprocessing system according to claim 5 wherein said lightbox includes aconcave surface and wherein said articulated facet is locatedposteriorly to said concave surface.
 12. A keratoscope image processingsystem according to claim 5 further comprising means for adjusting thepower output of said laser.
 13. A keratoscope image processing systemaccording to claim 1 wherein said conical body includes a disc oftranslucent material disposed in said bore to receive a portion of thelight introduced into said concavity and a plurality of light-perviousmachine readable spots arranged on said disc.
 14. A keratoscope imageprocessing system according to claim 1 wherein said lightbox includes akey for maintaining said conical body in alignment with said lightbox.15. A keratoscope image processing system according to claim 1 whereinsaid conical body includes a disc of translucent material disposed insaid bore to receive a portion of the light introduced into saidconcavity, and said lightbox includes a recess for receiving said baseportion of said conical body, a plurality of light-sensing diodesdisposed to monitor the light transmitted through said disc, and meansfor coupling an output of said light-sensing diodes to said processingmeans, said processing means being responsive to said output tocompensate for said series of opaque and light transmitting ringsidentified by said pattern.
 16. A keratoscope image processing systemaccording to claim 15, said system including means for storing a signalvalue representing a predetermined type of illuminated ring device, andmeans responsive to said output of said diodes including means forcomparing said output with said signal value for modifying saidprocessing of said keratoscope image.